1. Field of the Invention
The present invention relates to methods of manufacturing inductors, and more particularly, to methods of manufacturing inductors which can be used in a noise filter, a transformer and a common mode choke coil.
2. Description of the Related Art
A known laminated type inductor 1 for use in a noise filter is shown in FIG. 21 and FIG. 22. As shown in FIG. 21, the conventional inductor 1 includes a plurality of magnetic sheets 2 having a plurality of conductor patterns 11a-11d provided on surfaces thereof. A magnetic sheet 3 serves as a cover for covering the magnetic sheets 2. The conductor patterns 11a-11d are connected to define a spiral coil 11, by way of a plurality of via holes 14a-14c formed through the plurality of magnetic sheets 2. In this way, upon laminating together the magnetic sheets 2 and the top magnetic sheet 3 in a predetermined manner as shown in FIG. 21, it is necessary to perform a sintering process of the entire laminated structure to produce a laminated body 7 as shown in FIG. 22. Further, one end surface of the laminated body 7 is provided with an input electrode 10a of the coil 11, while the other end surface thereof is provided with an output electrode 10b of the coil 11.
However, with the above conventional inductor 1, since each of the conductor patterns 11a-11d has only a small thickness and hence has only a small cross sectional area, the coil 11 has only a small current capacity which allows an electric current to flow therethrough. Further, in a process of manufacturing the conventional inductor 1, since it is required to form a plurality of conductor patterns 11a-11d, the whole manufacturing process must include a large number of steps which results in a high manufacturing cost.
In order to overcome the problems described above, preferred embodiments of the present invention provide improved inductors each having an increased current capacity and each being constructed to be manufactured at a very low cost.
According to one of the preferred embodiments of the present invention, an inductor includes a coil assembly having an electrically conductive wire or a magnetic core member and an electrically conductive wire wound around the magnetic core member, the coil assembly being provided within a magnetic sintered body which has been formed by molding a ceramic slurry into a predetermined shape and sintering to produce a magnetic sintered body, and end portions of the electrically conductive wire are electrically connected to external electrodes provided on outer surfaces of the magnetic sintered body.
In using the above inductor having the above-described structure, a magnetic sintered body which has been formed by molding a ceramic slurry into a predetermined shape and sintered, functions as a path of a magnetic flux generated by the electrically conductive wire. Further, since the electrically conductive wire has a relatively large cross section which is larger than that of the conductor patterns of a conventional laminated type inductor, the electrically conductive wire has a greatly reduced direct current resistance, thereby significantly increasing the current capacity of the inductor.
Further, according to additional preferred embodiments of the present invention, there is provided an inductor in which a plurality of coil assemblies each being electrically independent from each other and including a magnetic core member and an electrically conductive wire wound around the magnetic core member, are contained within a magnetic sintered body which has been formed by molding a ceramic slurry into a predetermined shape and sintering to produce a magnetic sintered body, thereby forming an array type inductor having a greatly increased current capacity. Moreover, since either a plurality of non-magnetic members or a plurality of internal spaces are provided between the plurality of coil assemblies in the magnetic sintered body, formation of a magnetic circuit between each pair of adjacent coil assemblies is effectively prevented by either the non-magnetic members or the internal spaces. In this way, a desired result is reliably provided. That is, a magnetic flux generated by one coil assembly will not form an interconnection with another magnetic flux generated by an adjacent coil assembly.
Further, according to additional preferred embodiments of the present invention, there is provided an inductor in which at least one pair of mutually electrically connected coil assemblies, each including a magnetic core member and an electrically conductive wire wound around the magnetic core member, are contained within a magnetic sintered body which has been formed by molding a ceramic slurry into a predetermined shape and sintering to produce a magnetic sintered body. As a result, it is possible to form an inductor having an increased current capacity, which is suitable for use as a transformer or a common mode choke coil. At least one pair of coil assemblies may be formed either by winding a plurality of electrically conductive wires around one magnetic core member or by winding a plurality of electrically conductive wires around a plurality of magnetic core members.
Usually, when an inductor having a plurality of coil assemblies is used as a transformer or a common mode choke coil, the following phenomenon will occur in an area of a magnetic sintered body between two adjacent coil assemblies. More specifically, a part of a magnetic flux which has been generated by one coil assembly but does not form an interconnection with a magnetic flux generated by the other assembly, will enter into and exit from an area located between the two coil assemblies, thereby forming a magnetic circuit of a magnetic flux which contributes only to a self-inductance. In view of this phenomenon, if a non-magnetic member(s) or an internal space(s) is provided between the at least one pair of coil assemblies, a part of the magnetic sintered body between the at least one pair of coil assemblies, will have a higher magnetic resistance, thereby effectively preventing any entering and exiting of a magnetic flux with respect to this area. In this way, the non-magnetic member(s) or the internal space(s) effectively prevent any formation of a magnetic circuit of a magnetic flux which contributes only to a self-inductance. As a result, a large part of a magnetic flux generated by one coil assembly will form an interconnection with a magnetic flux generated by the other assembly. More specifically, within the magnetic sintered body, a magnetic flux is created so as to have an interconnection with adjacent coil assemblies. That is, the magnetic flux creates a magnetic circuit of a magnetic flux which contributes to both a self-inductance and a mutual inductance.
Further, according to additional preferred embodiments of the present invention, a method of manufacturing an inductor includes the steps of preparing a slurry for use in a wet pressing treatment and containing a magnetic ceramic material, introducing the slurry into a mold which already contains therein at least one electrically conductive wire or at least one coil assembly each including a magnetic core member and an electrically conductive wire wound around the magnetic core member, and performing the wet pressing treatment to obtain a magnetic molded body, sintering the magnetic molded body containing the at least one electrically conductive wire or the at least one coil assembly so as to form a magnetic sintered body, and forming on outer surfaces of the magnetic sintered body external electrodes electrically connected to end portions of the at least one electrically conductive wire.
With the use of the above method, i.e., a wet pressing method according to at least one preferred embodiment of the present invention, an inductor is manufactured via a greatly simplified process with a reduced cost, without having to use a complex process, such as that used to produce a laminated type inductor of the related art, which involves printing conductor patterns and laminating together a plurality of magnetic sheets. Further, since the slurry is sufficiently pressed during the wet pressing treatment, water contained in the slurry may be sufficiently removed therefrom, thereby effectively preventing formation of air bubbles within the slurry and thus ensuring a good quality for a molded product. In addition, since the electrically conductive wire is wound around the magnetic core member, any deformation of the electrically conductive wire is reliably prevented.
Further, a method for manufacturing an inductor according to additional preferred embodiments of the present invention is such that the method includes the steps of introducing a batch of slurry into a mold to perform a wet pressing treatment to produce a magnetic molded plate, forming a plurality of coil assemblies each having a magnetic core member and an electrically conductive wire wound around the magnetic core member or at least one coil assembly having an electrically conductive wound wire, fixing the coil assemblies or the at least one coil assembly having the electrically conductive wound wire on the magnetic molded plate, introducing another batch of slurry into a mold in which the magnetic molded plate has been placed, and performing the wet pressing treatment so as to obtain a magnetic molded body containing the coil assemblies. With the use of such a method, it is possible that after a plurality of coil assemblies have been fixed on a magnetic molded plate, the magnetic molded plate may be placed into the mold for forming the magnetic molded body. As a result, it is not necessary to directly place the plurality of coil assemblies into the mold, thereby ensuring an improved productivity for manufacturing the inductors.
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.